New York State Earth Science RegentsNew York State Living Environment Regents

 
Physical Behavior of Matter
Chemistry Regents June 2005 - Question 06 Print E-mail
chemjune05q06

Correct Answer: (4) form an aqueous solution

Why:

A physical property is one that can be measured without changing the composition of the matter.  These include appearance, texture, odor, color, melting point, boiling point, solubility just to name a few.  A physical change can occur such as changing from solid to liquid or liquid to gas.  It is still a physical change because the same element or compound is present before and after the change.  In other words the same molecule is present throughout.  A chemical property or chemical change is different because it concerns how the element or compound reacts with something else to make something new.  (4) is the correct answer because it is the property of its solubility and is not reacting with anything or changing its composition.

Answering this question:

A possible way to answer this question is to remember that a physical property has to do with the properties that do not inherently change the element itself, i.e. form it into a new compound or element.  This would allow you to quickly choose answer (4) because it is the only offered solution that did not involve a reaction.

So by looking at the answers and choosing the one that was most different from the others, (4) would stand out to you as the only one not being a reaction. In this case that would be the best possible choice.

 
Chemistry Regents June 2005 - Question 07 Print E-mail
chemjune05q07

Correct answer: (1) Iron

Why:

All metals are malleable and conduct electricity.  This is a question where looking at the periodic table will help you classify the characteristics of the elements, and discover which ones are the metals.

With the exception of Hydrogen (H) the periodic table has all its various metals to the left and middle.  There is a stair-stepping line of elements beginning with B (Atomic Number 5) going down to Si(14) then to Ge(32) and As(33), further down to Sb(51) and Te(52) ending at Po(84).  All of these compromise the Metalloids.  Everything to the Right of the metalloids is non-metals, including the very last group (vertical line) which is the noble gases.

Locating the possible answers on the periodic table will reveal only one possible metal and the correct answer (1) Iron (Fe)

Answering this question:

To answer this question you must remember that metals are the elements that have the physical characteristics of conducting electricity and being malleable.  This shouldn't be too hard to remember because we've all learned that metals conduct electricity and can be formed into things such as cars, tin foil, or washing machines.

You may not remember the proper symbols for the elements named to locate them on the periodic table, or you may not remember where the metals can be found on the table, however, that does not make this question impossible.  Iron should stand out rather quickly as being a well known metal.  Do not be worried if you could not recognize and rule out any of the other answers.  You have to choose only one answer in this example, and you've already found a correct one you can be fairly sure of.  There are no "all of the above" choices, or "(1) and (3)" answers so you're safe!

 
Chemistry Regents June 2005 - Question 14 Print E-mail
chemjune05q14

Correct Answer (1) temperature of the solution increases

Why:

It is a general principle that the solubility of a solute in a solvent such as water increases with the temperature going up to a 100 C.  Pressure only becomes a concern in the solubility of a solute if the solute is a gas and then it is directly proportional to the partial pressure of the gas above the solvent.  Therefore the best answer to this question is (1) the solubility increases with increasing temperature.

Answering this question:

The first determination you must make is if pressure or temperature matter in this situation.  The equation shows you that the solute is a solid and so pressure can be eliminated immediately.  Using everyday experiences, we realize things dissolve faster in hot water.  Sugar dissolves much more quickly in coffee than ice tea. We also can stop and think about what is happening to water when it warms up. The particles are moving faster and have more space between them to dissolve the solid better.  Therefore (1) is the best answer.

 
Chemistry Regents June 2005 - Question 15 Print E-mail

chemjune05q15

Correct Answer:  (2) higher boiling point and a lower freezing point

Why:

The capital M, when referring to an aqueous solution is its Molarity, or concentraion.

Generally as the molarity of a solution increases the boiling point increases and the freezing point decrease.  The boiling point is higher because the solute lowers the vapor pressure of the solution.  The solution can not boil until its vapor pressure reaches the atmospheric pressure, so it takes longer to catch up.  The freezing point is lower because the solute gets in the way of the molecules forming a solid lattice.  Therefore the molecules take longer to freeze into a solid.

Answering this question:

The best way to answer this question is just to know it.  A simple way to remember is to think about salt and water.  It is harder to boil salt water and it is harder to freeze salt water. It is possible to eliminate two answers relatively easy.  If the "salt" in the solution was going to make it harder or easier to boil water it would also make it harder or easier to freeze.   It is unlikely that it would help in one phase change but then get in the way of another.  So you can eliminate answers (1) and (4). If you were completely unsure, the best way to tackle this problem is to decide whether or not you think the "salt" being in the water would deter it from or help it to boil/freeze.   It seems reasonable that having something interfering with the normal dynamics would make it harder and therefore the boiling temperature would go up and the freezing temperature would go down making them both harder to achieve.

That leaves you with answer (2)

 
Chemistry Regents June 2005 - Question 16 Print E-mail
chemjune05q16

Correct Answer:(1) are in random, constant, straight-line motion.

Why:

The Kinetic molecular theory for an ideal gas makes several assumptions.  The gas consists of very small particles with non-zero mass.  The number of molecules is large so that statistics can not be applied.  The molecules are in constant random motion. The rapidly moving particles constantly collide with the walls of the container.  The collisions of the gas particles with the walls of the container are perfectly elastic. The interactions among molecules are negligible.

Therefore the best answer that matches these assumptions is (1).

Answering this question:

If you know the kinetic molecular theory and what it assumes the best way to handle this problem is to find the answer that matches.  If you don't know all of the assumptions of the kinetic molecular theory it is necessary to look at what we know about gases and eliminate some answers. Let us think of a blown up balloon.  Beginning with (4) - If the system lost energy it would have to escape somewhere into the environment or the walls it is colliding with.  But I've never felt a balloon inexplicably get warmer.   For answer (3), if the gas particles had strong attractive forces to one another they would not be a gas.  They would enter another state (liquid or solid) and the balloon would deflate.  Answer (2) has an arranged geometric pattern.  If this were true the balloon would conform to the geometric shape the gas was forcing it to become.  This leaves us with answer (1) random, constant, straight line motion.  This does make sense.  We envision gas particles moving around randomly hitting the walls, that is what keeps the balloon inflated and makes the gas conform to the container it is in.  Therefore we can reason out answer (1) even if we don't remember the kinetic molecular theory.

 
Chemistry Regents June 2005 - Question 17 Print E-mail
chemjune05q17

Correct Answer (2) Sublimation

Why:

Sublimation is the transition from the solid to the gas phase bypassing the intermediate liquid stage.  This transition is endothermic and requires temperatures and pressures below the triple point.  The opposite of sublimation is deposition.  That would be the transition from gas to solid and bypassing the liquid phase a gain and is common in meteorology.  Solidification is transitioning from liquid to solid, and condensation is transitioning from gas to liquid.

Answering this question:

Condensation and solidification are pretty frequently described transitions.  We often here about the condensation on windows, or water solidifying to ice so we should be able to eliminate these two answers quickly.  Between the two remaining choices you have to know what sublimation is, otherwise you're making an educated guess and at least have doubled your chances.

 
Chemistry Regents June 2005 - Question 38 Print E-mail
chemjune05q38

Correct answer: (3) Ca3(PO4)2

Option no. 2, KC2H3O2 and option no. 4, Ca(NO3)2 are eliminated because they both have no exceptions in terms of solubility in water.  As seen in Table F, acetate (C2H3O2-) and nitrate (NO3-) ions form compounds that have no exceptions in terms of solubility in water.

Option no. 1, K2CO3 is eliminated because it is also soluble in water.  The carbonate (CO32-) ion forms insoluble compounds EXCEPT when combined with Group 1 ions or ammonium (NH4+).  In this case, CO32- is combined with K+ which falls under Group 1.

Option no. 3, Ca3(PO4)2 is answer being the least soluble in water.  Table F shows that phosphate ions (PO43-) form insoluble compounds EXCEPT when combined with Group 1 ions or ammonium (NH4+).  In this case, Ca2+ does not belong in Group 1 but in Group 2 which leads us to therefore conclude that Ca3(PO4)2 as the least soluble.

 
Chemistry Regents June 2005 - Question 41 Print E-mail
chemjune05q41

Correct answer: (1) KI

Reference Table G shows various solubility curves for various substances in 100 g of H2O at various temperatures.  This illustrates how a certain solute behaves at a certain condition when dissolved in water.

A saturated solution is defined as the maximum amount of solute that will dissolve at that specific temperature.  This condition lies on a point of the solubility curve.

On the other hand, if your condition lies below the solubility curve, the solution can still handle more solute and it is said to be unsaturated.  If the condition falls above the curve, it represents supersaturation.  This supersaturated solution holds more solute that can normally dissolve in the present volume of solvent.

Answering the question:

Option no. 2, KNO3 is eliminated because at 10°C with 80 g of the substance dissolved in 100 g of H2O, the solution is already supersatured.  The said condition is found above KNO3's solubility curve.

Option no. 3, NaNO3 is eliminated because the solution is saturated at the given condition of 10°C with 80 g of the substance dissolved in 100 g of H2O.  The condition is found in one point of its solubility curve.

Option no. 4, NaCl is eliminated because at the given condition, it is supersaturated as well with the condition found above its solubility curve.

This leaves us with option no. 1, KI as the answer.  The solution in the given condition is unsaturated since it will only reach saturated condition at 10°C with approximately 137 g of the substance.

 
Chemistry Regents June 2005 - Question 43 Print E-mail
chemjune05q43

Correct answer: (3)

A particle diagram is a representation of atoms, molecules, compounds, mixtures, etc.

The phase of matter should be determined to come up with a diagram.  For solids, the particle diagram appears to be packed while those for liquids, particles are slightly apart.  A particle diagram for a gas shows the particles quite far apart.

Answering the question:

As mentioned, the molecules to be represented by a particle diagram is a 2-element gaseous compound.

Option no. 1 is eliminated because as seen in the diagram, it represents a single element and not a compound.

Option no. 2 is eliminated because the diagram represents only two elements and not a 2-element compound.

Option no. 4 is eliminated because the diagram shows 2 different types of 2-element compound.

This leaves us with the correct answer of option no. 3.  The particle diagram fits exactly the 2-element gaseous compound criteria.

 
Chemistry Regents June 2005 - Question 46 Print E-mail
chemjune05q46

Correct answer: (1)

Fluorine and Iodine both belong to a group of elements known as halogens. They share similar properties as a result of the number of available electrons in their valence orbital. However, fluorine is first of the halogens in the periodic table and has an atomic number of nine (9), while iodine is one of the last halogens and has an atomic number of fifty three (53). Iodine as a result has a much greater number of electrons at 53 than fluorine at 9. Intermolecular or Van Der Waals forces are responsible for the formation of liquids and solids when they are greater than the kinetic energy of the molecule. The intermolecular forces are also generally stronger for molecules that contain a greater number of electrons as is the case for iodine.

Answering the question:

When answering this question there are two things that should be understood beforehand.

Firstly an idea of where on the periodic table iodine is relative to fluorine. The fact that the question states that fluorine is a gas and iodine is a solid is an indicator that iodine is probably lower down the group in periodic table than fluorine.

Secondly it would be important to understand the interaction between kinetic energy and intermolecular forces. Kinetic energy is the energy that would keep the molecules in motion, however intermolecular forces are the forces of attraction that one molecule would have with another when they are close enough to each other. When the intermolecular forces of attraction are able to overcome the kinetic energy then a liquid or solid is the result.

Therefore when comparing why a molecule exists as a gas or a solid the intermolecular forces play a greater role than the kinetic energy leaving only (1) and (2) as the possible answers. The intermolecular forces of fluorine have to be weaker than those of iodine in order for fluorine to be a gas and iodine a solid.

This leaves (1) as the correct answer

 
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